The average person is not a technologist. They don’t spend time learning operating system internals — they just want to use a device.
Android devices only get updates for the first year — if even that long. Apple iPhone get iOS updates for 5 years — guaranteed. If you buy an iPhone you don’t need to learn how to install something like cyanogenmod to keep your phone up to date. You don’t need to worry about reflashing your phone either. When you buy a used Android, it could have spying software installed, and you would never know it unless you reflashed the phone.
With iOS, simply performance a factory reset, and all third party software is gone. And if you want to reflash your phone, just put in in DFU mode and dock it to iTunes. The software will take care if everything else for you.
Take a look at the iPhone 5S. The iPhone 5S was released in September of 2013. It originally shipped with iOS 7.
It currently runs iOS 12, and received its last update on September 26th, 2019. iOS 12 is able to run almost every app that the newest versions of iOS can run.
Now lets look at the Samsung Galaxy Note 3, which was also released in September 2013. It shipped with Android 4.3 and currently runs Android 5.1.1, which came out in February 2015, giving the Note 3 17 months of support.
People trust buying used iPhones but not used Androids because iPhones stay supported much longer than Android do. Because they run newer versions of iOS, they have more security features and are able to use many modern apps.
- Build Quality I think this will change in the future but older(~2015) iPhones had better build quality than Androids.
- Software Updates this is the usual answer at this question. (~5 years support vs 2 years)
- Power iPhones tend to be overpowered given their system. iOS is a very optimized OS and consumes very little resources compared to Android. Meaning that older iPhones can easily run the newer iOS while Android phones are lagging behind.